WASHINGTON, Aug 7 (Reuters) - The United States has approved military air drops of humanitarian supplies in northern Iraq for religious minorities fleeing attacks by Islamist militants and they could start at any time, a senior U.S. official said on Thursday.

Officials said President Barack Obama was also weighing carrying out the first U.S. airstrikes in Iraq since a 2011 pullout of troops.

Speaking on condition of anonymity, the officials said the United States was considering acting amid international concern over the fate of 40,000 members of religious minorities driven out of their homes and trapped on an Iraqi mountaintop under threat from the militants.

U.S. government sources said the United States would be flying surveillance drones out of the Kurdish capital Arbil as part of a mission to assess the Islamic State threat and the capability of Iraqi and Kurdish forces to confront it.

White House spokesman Josh Earnest told reporters earlier that Obama had met members of his national security team on Thursday. Earnest declined to say whether U.S. military intervention in Iraq was being considered.

Any airstrikes would represent the first combat action by the United States in Iraq since it ended eight years of war in 2011. Earlier this year the United States sent in a small number of military advisers to help the Iraqi government address the threat of the Islamic militant offensive.

Earnest said Obama had made clear in the past that any U.S. military action would be "very limited in scope," would not involve putting troops on the ground, and should be closely tied to Iraqi political reforms, which Washington has demanded.

"We're working intensively with the government of Iraq - the Iraqi security forces and the Kurdish authorities in the immediate area to support their efforts to address the humanitarian situation in Sinjar," Earnest said.

Although he declined to directly address the issue of possible U.S. action at Sinjar, Earnest stressed the strict limits of any U.S. military involvement in Iraq. "There are no American military solutions to the problems in Iraq," he said.

The Islamic State's Sunni militants, an offshoot of al Qaeda who have swept across northwestern Iraq in recent weeks, have come within a 30-minute drive of Arbil. The Islamic State views as infidels Iraq's majority Shi'ites and minorities such as Christians and Yazidis, a Kurdish ethno-religious community.

Near the White House, some 80 people protested for hours on behalf of the Yazidis, shaking U.S. flags, chanting slogans and holding up signs condemning what they called a holocaust of Christian communities in Iraq and Syria by the Islamic State.

U.S. SAYS BAGHDAD RESPONSIBLE

Some of the many thousands trapped on Sinjar mountain have been rescued in the past 24 hours, a spokesman for the U.N. Office for the Coordination of Humanitarian Affairs said earlier, adding that 200,000 had fled the fighting.

Earnest said the responsibility for the humanitarian crisis in Iraq, including that on Sinjar mountain, lay with the Iraqi leaders who had failed to create a united government to address the interests of the country's Shi'ites, Sunnis and Kurds.

The Islamist fighters, who have killed many thousands and declared a caliphate in the Iraqi area they conquered, are now threatening Kurdistan, previously considered a bastion of stability in a country ravaged by conflict.

Bernadette Meehan, spokeswoman for Obama's National Security Council, told Reuters on Wednesday that any provision of U.S. weapons to the Kurds "must be coordinated with central government authorities, in Iraq and elsewhere."

But she added that given the threat from the Islamic State, "the United States will continue to engage with Baghdad and Arbil to enhance cooperation on the security front and other issues." (Additional reporting by David Rohde, Doina Chiacu, Mark Hosenball and Annika McGinnis in Washington; Editing by David Storey and Howard Goller)

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